Multimeter – basic functions
Multimeter – basic functionsDate of publication: 02-07-2025 Update date: 10-04-2026 🕒 9 min read
Piotr Górecki – electronics enthusiast. Currently, he publishes his own magazine "Understanding Electronics." Previously, he was the Editor-in-Chief of a popular Polish magazine (Electronics for Everyone) for many years. He is also the author of hundreds of articles and educational projects. Until 1993, he worked in the telecommunications industry.
Here is the first of three articles intended for beginners, dedicated to multimeters. We will discuss various functions of these meters and provide numerous tips for electronics enthusiasts who want to learn more about multimeters and make purchases of such devices.
Table of Contents
- What is a multimeter used for?
- Switching functions and ranges
- Measuring DC and AC voltage
- Measuring resistance (continuity or break)
- Measuring DC and AC current (amperage)
- Safety issues
- Categories CAT I…CAT IV
In every modern home, a multimeter, a universal electrical measurement device, is useful. The cheapest multimeters can be bought in supermarkets for about 20 zlotys. They are sufficient for basic measurements. However, it's worth spending a bit more to buy a significantly better version.
What is a multimeter used for?
As the name suggests, a multimeter is a "multi-meter" that can primarily be a voltmeter for measuring voltage and an ammeter for measuring (amperage) current. It can also be an ohmmeter, a meter for measuring resistance expressed in ohms resistance. Most multimeters also allow measuring various other quantities (diode forward voltage, capacitor capacitance, temperature) and testing some components (diodes, bipolar transistors). Therefore, a multimeter is rightly called a universal meter. For several decades, digital multimeters have dominated the market. An example of using an (older) multimeter is shown in the title photograph.
We most often measure the voltage of batteries and accumulators, less frequently the voltage (in the socket) of the power grid. We often measure resistance, or rather check if it is very low, to ensure there is continuity, a short circuit, or a break, meaning an open circuit, lack of connection.
We often talk about current, but we relatively rarely measure its value – more precisely – the current intensity.
Switching functions and ranges
In every multimeter, the user must select the function, i.e., what they want to measure. In simpler multimeters (photograph 1), you also need to select a specific measurement range with a knob.
Photograph 1
In multimeters with automatic range switching – examples in photograph 2 – you only select the function, and the multimeter will automatically switch to the needed range during measurement.
Photograph 2
Currently, most, if not almost all, more expensive multimeters have automatic range switching. Interestingly, in certain quite common situations, many electronics enthusiasts consider this more of a disadvantage than an advantage.
Here are the most commonly performed measurements.
Measuring DC and AC voltage
A multimeter in the role of a voltmeter is used to measure voltage, expressed in volts, occurring between two points. We most often measure DC voltage (DC) with a multimeter, e.g., battery voltage, accumulator voltage, power supply voltage. The simplest practical rule for batteries and accumulators is this: if the measured voltage is lower than the nominal voltage, the battery is significantly discharged. For example, a new 1.5V battery has a voltage of over 1.6 volts – example in photograph 3.
Photograph 3
If the measured voltage is higher than the currently set range, the display will show an overload indication, often in the form of a lit "1" on the display, the letters OL – OverLoad (photograph 4), sometimes in the form of horizontal dashes or otherwise. The same applies to current and resistance measurements. Only in a few more expensive multimeters is the overload also signaled by sound. Importantly: in digital multimeters, exceeding the range when measuring voltage does not risk damage – details in subsequent articles in this series.
Photograph 4
We less frequently measure AC voltage (AC), also expressed in volts, e.g., the output voltage of a transformer or the voltage in a 230V power socket. Then you need to switch the multimeter to measure AC voltage, indicated by the abbreviation AC or VAC. When measuring higher voltages, dangerous to humans, to minimize the risk of electric shock, it is worth taking measurements with one hand. This way, there is no possibility that, due to user error, current will flow between two hands through the heart – example in photograph 5.
Photograph 5
Measuring resistance (continuity or break)
A multimeter can measure resistance (in ohms). For such measurements, it is worth using small crocodile clips of the 2mm standard – example in photograph 6.
Photograph 6
Importantly, almost every multimeter has a built-in buzzer and either on the lowest resistance range or on a separate range performs an additional function – acoustic continuity, short circuit indication meaning very low resistance – photograph 7. If the tested resistance on this range is less than a few dozen ohms (varies for different meters), the buzzer sounds. In practice, this is very often useful for checking if, for example, a wire (cable) is not broken or if there is no short circuit between its conductors.
Photograph 7
Measuring (amperage) DC and AC current
The average user most often measures voltages and much less frequently uses a multimeter to measure current, more precisely to measure current intensity (in amperes). To measure current (current intensity), you need to break the circuit and insert an ammeter there, as illustrated in diagram 8.
Diagram 8
This is a significant complication that is not present in voltage measurements. An example might be measuring the current draw from a car battery when parked, when everything is turned off – theoretically, the current draw should be zero, but in practice, some current is drawn by the alarm system, and too high a draw at rest will quickly discharge the battery. Sometimes, current draw from other batteries is measured. Photograph 9 shows the measurement of current drawn by a section of a 12-volt LED strip.
Photograph 9
Safety issues
It is advisable to avoid measuring current in 230V AC power circuits due to the increased risk of fatal electric shock. Here are some warnings related to this.
AC voltages up to 24 volts (24 V AC) and DC voltages up to 60 volts (60 V DC) are considered fully safe. Many people have found that voltages up to 100V do not pose a risk of death. The 230V power grid voltage is certainly deadly dangerous! I personally knew several people who are no longer alive because they were fatally electrocuted by 230V grid current. Of course, due to their own fault, due to lack of caution.
Generally speaking, any, even the cheapest, multimeter allows measuring 230V AC grid voltage. The maximum voltage value measured by a multimeter is usually 600V, 750V, or 1000V. A separate issue is the risk of damaging the meter with incorrect function and range settings.
Minors and beginners should only perform work related to circuits where dangerous voltage is present under the supervision of qualified supervisors!
When measuring in circuits with voltages greater than 100V, especially in power grid circuits, always maintain special focus and caution! Due to the risk of fatal electric shock, measurements should always be conducted in the presence of a second person, who is informed in advance about what to do in case of an accident – how to quickly disconnect the power.
The second general rule: measurements of dangerous voltages should be conducted with one hand, so that in case of an accident, current does not flow between hands through the heart. This is illustrated in the earlier photograph 5. Initially, this may seem strange, unnatural, and quite troublesome, but it is worth getting used to it, and then keeping the other hand behind your back or in your pocket. Although measurements taken with one hand do not eliminate the risk of shock (on the path between the phase wire and the ground), they significantly reduce the risk of an accident.
Categories CAT I...CAT IV
A separate issue is the safety category of the meter: CAT I...CAT IV (the higher, the better). CAT category issues are discussed in more detail in the article marked Q006.
Generally, these categories concern measurements in various sections of the power grid. They do not concern measurements in circuits inside devices, only directly in power grid circuits. Therefore, CAT categories are very important for electricians and much less so for electronics enthusiasts.
Older, fully usable multimeters, do not have a specific CAT category at all. Many of the new ones do not have a CAT designation and stamp either, stamp on many new multimeters, but possibly other related terms - examples in photo 10 and photograph 11.
Photograph 10
Photograph 11
When purchasing a new multimeter that would also be used for measuring voltage and current in the 230 V grid, including socket voltage, the minimum category is CAT II 300 V, better CAT II 600 V or even higher. The CAT III designation indicates that the meter can also be used for measurements in a three-phase power grid.
In the second article of this series (B041), we will discuss other functions of multimeters, and in the third, we will address questions and doubts related to multimeters.
©
Piotr Górecki
Disclaimer:The contents of this article are for informational purposes and do not constitute technical advice or a substitute for appropriate training. When working with electrical and electronic equipment, always observe applicable Health and Safety regulations and follow the manufacturer's recommendations and operating parameters.
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